Open Shortest Path First (OSPF) protocol is a routing protocol that is commonly used in intelligent optical networks. Each router which runs OSPF protocol distributes its local link state information throughout the Autonomous System by flooding, and ultimately every participating OSPF router can obtain all the link state information of the whole Autonomous System's topology, and all the OSPF routers have the same link state database.
The flooding of OSPF link information is implemented via various Link State Advertisements (LSAs). The standard OSPF LSAs are: Router-LSAs, Network-LSAs, Area Border Router-Summary-LSAs, Autonomous System Boundary Router-Summary-LSAs, AS-external-LSAs, etc. In order to meet the requirements of Traffic Engineering (TE), OSPF extension protocol is used to extend the standard LSA, i.e., by using Type 10 Opaque LSA for releasing related link information, which is called Traffic Engineering Link State Advertisement (TE LSA).
The TE LSA, which is an opaque LSA, has two kinds of top-level TLVs (Type/Length/Value): Router Address TLV and Link TLV. Wherein, the Link TLV mainly describes the link properties of Traffic Engineering (TE) and defines standard sub-TLVs numbered 1 to 16, i.e., secondary TLVs, which include Link Type, Link ID, Local interface IP address, Unreserved bandwidth, Link Protection Type, Shared Risk Link Group, Interface Switching Capability Descriptor, etc; wherein, the link protection type is No. 14 sub-TLV.
According to the IETF definition, the protection type of the links in an automatic switching optical network includes Extra Traffic, Unprotected, Shared, Dedicated 1:1, Dedicated 1+1, Enhanced, etc. When an optical fiber is configured with Multiplex Section Protection (MSP), protection types of channels in the fiber can be categorized into three types: Enhanced, Unprotected and Extra Traffic; that is, protection types of different channels in an optical fiber can be different from each other, so it is inappropriate for a fiber link to define only one protection type.
Presently, when an optical interface is configured with MSP, the links for the bidirectional shared multiplex section can be divided into three TE links of different attributes: enhanced TE link, extra traffic TE link and unprotected TE link. In this way, the protection types of all the bandwidth resource for each TE link are identical. The three TE links generate LSAs to be flooded respectively.
It can be seen from the above mentioned representations:
(1) when there is traffic on a link, a multiplex section can not be dynamically configured, modified or deleted in this link, because configuring, modifying or deleting the multiplex section can result in regeneration of the TE link index for the optical interface. For example, if no multiplex section is configured initially, there exists an unprotected TE link in the optical interface; when multiplex sections are configured, the original TE link is deleted and then three new TE links are generated in accordance with the new configuration. In this way, the meaning of the link TE index for the current traffic stored in signaling has changed, which may likely cause the index to not relate to the original TE link.
(2) one optical fiber is represented by three TE links, resulting in large number of TE links and much flooded information, which increases the burden of the network.